The tunnel work turned out to be much more difficult than the builders had planned on. In the autumn of 1994, the situation became dramatic. Saltwater gushed out from a borehole, at a rate of about two hundred litres per minute. Along with the water, loose sand and coal fragments entered the tunnel. It appeared that the tunnel workers had come into contact with a roughly 10 metre-wide zone containing loose remains of coal, sand, sandstone and conglomerate.
Though the tunnel-builders despaired, the researchers were very happy for this discovery. The up to 20 cm- large coal fragments are the remains of a coal layer that had been broken up by fault-movements after being deposited. Probably, there was a tree covered coastal plain in this area during the Jurassic Period. Some of the coal fragments are identified as parts of tree trunks or branches, where the structure of the tree is still partially visible. In the sandstones, pollen and spores have been found which indicate delta- or swamp vegetation. There are also finds of microfossils from marine microrgansims.
Analysis of pollen and spores shows that the layers were laid down in late Jurassic time, and are between 155 and 160 million years old. The corresponding layers in the Troll Field are mostly flat-lying. The Bjorøy layer is both tilted on its side and broken due to movements along a fault zone. There have been several episodes of earthquakes, both before and after the Jurassic layer got deposited. It is also exciting to realize from this history that we can expect new earthquakes at Vatlestraumen in the future.
